A cause can be identified in about 5% of hypertension cases. Such cases are referred to as "secondary hypertension", this name reflecting that the high blood pressure in question is secondary to (caused by) some other underlying disease state. Examples of conditions that can cause secondary hypertension follow:
- Renal Artery Stenosis. This condition occurs when the artery that leads to the kidney narrows and blood flow to the kidney is reduced. In response the kidney releases chemical signals that cause blood pressure to raise throughout the body so as to increase blood flow to the kidney. The arterial narrowing can be caused by atherosclerosis (hardening of the arteries, usually occurring in men over 45 years old) or by a condition called fibromuscular dysplasia (tissue changes in the artery wall, usually occurring in younger women).
- Kidney Failure. Kidney failure, occurring when the kidneys ability to filter blood is reduced, is associated with high blood pressure. Kidney failure causes a variety of problems affecting hormones, and water and sodium (salt) retention.
- Hyperaldosteronism. Aldosterone is a naturally occurring steroid made by the body. Hyperaldosteronism refers to too much aldosterone. Increased aldosterone causes increased salt retention which leads to high blood pressure. There two types of hyperaldosteronism. In primary hyperaldosteronism (also called Addison's Disease) the adrenal gland manufactures too much aldosterone. Secondary hyperaldosteronism occurs when a brain tumor causes the pituitary gland to signal for the release of excess aldosterone from the adrenal glands.
- Oral Contraceptives. On occasion, oral contraceptives (birth control pills) can cause increased blood pressure. Though usually subtle, in a minority of cases the effect can be dramatic.
- Sleep Apnea. In obstructive sleep apnea the airway is blocked off for small periods of time during sleep. The obstruction may lead to a multitude of problems including snoring and high blood pressure. Sleep apnea is often related to obesity which is itself a risk factor for hypertension.
- Intracranial Pressure. Intracranial is derived from two words- 'intra' which means 'within' and 'cranial' which means 'skull'. The word intracranial thus refers to something happening inside the skull, usually involving the brain. Pressure increases inside the skull may be caused by the presence of a mass (like a tumor) inside the brain, or fluid build-up around or within the brain (such as occurs when someone has a hemorrhagic stroke or has suffered head trauma). Increased intracranial pressure can make it more difficult for the brain to receive enough blood from the body. The brain compensates for increased pressure by raising overall blood pressure to the point where the brain remains properly supplied with blood.
- Stroke. It is fairly common in the aftermath of a strokes for blood pressure to become increased. As is the case with increased intracranial pressure, the increased blood pressure is the brain's way of compensating for the reduced blood flow to the brain that is associated with stroke.
- Pheochromocytoma. Pheochromocytoma is a relatively rare type of tumor that secretes chemicals which increase blood pressure.
Isolated Systolic Hypertension
Isolated systolic hypertension is present when systolic (heart beat) pressure is greater than 160 mmHg, but diastolic (heart rest) pressure is normal (80mmHg or less). The condition is generally related to hardening of the arteries (atherosclerosis).
Pregnancy is usually accompanied by a slight increase in blood pressure (which is considered normal). However, if the average blood pressure 15 mmHg or more above pre-pregnancy pressure levels, the label “pregnancy induced hypertension” is applied. In addition, there is a condition in pregnancy called ‘pre-eclampsia' which includes hypertension as a feature.
White Coat Hypertension
In white coat hypertension, high blood pressure is evident in the doctor's office but not at home. Visiting the doctor is stressful; white coat hypertension may account for upwards of 20% of mild high blood pressure cases. Though in the past thought to be benign, white coat hypertension has been shown to predict heart disease. Treating this mild form of hypertension may reduce the risk of future heart disease.